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AD9957 PLL

Question asked by SAURABH on Oct 11, 2012
Latest reply on Oct 12, 2012 by DSB

Hi

         i am using 20 MHz external CLK for AD9957 PLL input, but it is not locking  for frequency 800 MHz.it gives a 20-30 MHz wide signal at pin no 55.  centered around 320 MHz.(pll loop filter BW=2.5 MHz,VCO=4)when i change the  VCO from 4 to 5,it results increase in current & same spectrum shifted to around 400 MHz,pl suggest why PLL is not locking.

its ref clk circuit is working by verifying /8 output frequency & /4 output at pin no 55.

one more observation when loop filter is designed for 50 KHz ,the devices does not draw current.

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